Axial compressors



July 1, 1958 wElSE AXIAL COMPRESSORS Filed April 29. 1955 3 Sheets-Sheetl ATTORNE Y5 July- 1, 1958 A. WEISE AXIAL COMPRESSORS 3 Sheets-Sheet 2Filed April 29, 1955 I VENT 0K IRTUR W619i Ami mils A. WEISE AXIALCOMPRESSORS Jul 1, 1958 Filed April 29, 1955 s She ets-Sheet a ATTORNEYSUnited States Patent Cfilice AXIAL C(EEIPRESSORS Artur Weise, Ruit uberEsslingen, Germany, assignor to secrete Nahonaie dEtude at deConstruction tie Moteurs (lAVliifiGn, Paris, France, a French companyApplication Aprii 29, 1955, Serial No. 504,955 Claims priority,application France P/Iay 4, 1954 1 Claim. (Cl. 230-114) The increase inthe outputs of reaction units clearly necessitates a correspondingincrease in the output of the various members and in particular of theair compressor which, in the present state of the art, is mostfrequently of the axial type. Now, the usual types of axial compressors,such as have been constructed in the greater part of reaction motors,are complicated machines, comprising a fairly large number of wheelswhich act successively on the fluid to be compressed.

The two-fold requirement of increasing the rated output and of reducingthe overall dimensions has lead to the development of supersoniccompressors. The most simple machines of this kind spring from thefollowing considerations:

As is well known, if the triangles of speed (see Fig. '1) are consideredat the intake and at the outlet of an axial compressor Wheel, in whichtriangle u is the tangential speed at the mean diameter of the blading,v and W1 are the absolute and relative speeds of the fluid at the entryto the Wheel, v and W2 the absolute and relative speeds on the outletside of the wheel, the specific Work of compression in the wheel may beexpressed as follows:

If it is desired to increase the specific work of compression, either 11or A or Av can thus be varied or both these factors may be varied. Themechanical properties of the metals do not permit of any substantialincrease in the peripheral speed 1: with respect to the very high speedswhich are already employed; however, the vectorial difierence Av can beconsiderably increased if the moving wheel works with an average degreeof reaction in the vicinity of O, as is the case in the diagram of speedshown in Fig. 1. 'If a wheel of this kind is rotated at the speedemployed in the normal types of axial compressors, the speed v of thefluid discharged from the Wheel is supersonic, although the relativespeed W2 of the fluid in the wheel remains subsonic.

This supersonic flow thus creates the problem of a suitable constructionfor the fixed guiding blades, which are located on the delivery side ofthe moving wheel and act to convert the kinetic energy acquired by thefluid in the wheel into pressure energy. ,7

In accordance with the point of operation of the compressor, compressionor expansion waves are formed at the leading edge of these blades, thesewaves being comprised between two Mach lines which form, as is known, anangle with the direction of flow known as the Mach angle, the value ofthis being a function of the Mach number of the flow. Theseperturbations come in contact with the neighbouring blade, or pass infront of it, and are thus propagated towards the upstream side.

In the first case, that is to say when they strike the neighbouringblade and become reflected from it towards the interior of the grid ofblades, and thus towards the downstream side of the flow, the conditionsof the incident flow are not changed. In the second case, on the otherhand, that is to say when the incident flow and 2,841,325 Fatented July1, 1958 its direction are such that the waves which are produced 'passin front of the neighbouring blades and propagate themselves towards theupstream side, into the moving wheel from which they are reflected, theresult is that the flow becomes uncontrollable. Even if a supersoniccompressor does not exhibit such a phenomenon when it operates at thespeed for which it is adapted, it will however inevitably be met withwhile running up to speed from the position of rest.

The present invention has for its object a device for controlling theflow at the entry of a grid of blades which enables these drawbacks tobe overcome.

In this device, the blades are combined with shutters or orientableauxiliary blades which precede them and which can either form anextension of them on the upstream side, or be located opposite thespaces between the blades, the orientation of these shutters orauxiliary blades for certain working speeds of the compressor being suchthat the incidence of the flow with respect to the said auxiliary bladesis nil, and thus has a negligible eifect, and that in consequence thedisturbances due to the obstacle are also negligible.

In the case of auxiliary blades which preferably have afine and a sharpleading edge, it is convenient to choose a length of chord such that atall the useful speeds of operation of the compressor, a wave of acertain strength caused by a main blade strikes the auxiliary blade andis thus reflected so as to pass into the grid of main blades, thusavoiding a disturbing effect on the upstream side of the flow.

The auxiliary blades may be rigid and may comprise a point of rotation,either on the body of the main blades, or at any point located betweentwo main blades. The auxiliary blades may also be rigidly built-in alongtheir trailing edges, their leading edges being in this casebroughtiinto the direction of the indigent flow by an elasticdeformation which is preferably such that the first part of theseauxiliary blades which directly follows the leading edge, remainsstraight. The setting of the auxiliary blades may, for example, beobtained automatically, by using the difierence in pressure between theextrados and the intrados of the blades as the controlling force.

The description which follows below with regard to the attached drawings(which are given by way of example only and not in any sense by way oflimitation) will make it quite clear how the invention can be carriedinto effect, the special features which are brought out, either in thedrawings or in the text, being understood to form a part or" the saidinvention.

Fig. 1 is the diagram of composition of speeds in the moving wheel,which has already been referred to in the opening part of the presentdescription.

Fig. 2 is a diagrammatic view in axial cross-section showing the movingwheel of the compressor and the fixed blades which follow it.

Fig. 3 is a developed view of the blades of the wheel and of the fixedblading.

Figs. 4 to 6 show in a similar manner developed views of fixed bladesprovided with the improvement in accordance with the invention andshowing three diiferent forms of embodiment of this improvement.

Fig. 7 is a view to a larger scale of an embodiment in accordance withFig. 4 and shows a detail of a control device for the auxiliary blades.

I Fig. 8 is a partial cross-section of this device taken along H theline VlllVlH. In this Fig. 8, the line VIIVII shows the outline of theplane from which Fig. 7 is observed.

In Figs. 2 and 3, there is seen at 1 the blading of the moving wheel ofan axial compressor, the blades of which have a tangential speed 1: attheir mean diameter.

the crests of the leading edges.

-7a of the compressor (see Fig. 8).

the blades form channels between each other, these channels being firstof all'convergent-divergent from a to b in order to transform thesupersonic flow to a subsonic flow, and are then divergent from b to 0,playing the .part over this portion of the diffusion channels ofordinary compressor and converting the kinetic energy ofthe gas intopressure energy.

The direction of the leading edges 2a is determined in such manner thatat the normal speed of working of the compressor, the absolute speed vof the fluid passing out of the wheel is parallel to these leadingedges.

If the conditions of working are such that the absolute speed v of theflow makes 'a certain angle of incidence 'with the leading edges 2a, asis the case in Fig. 3, Mach lines shown by the chain-dotted lines 3 areproduced at As will be understood withreference to Fig. 3, these Machlines'are' propagated towards the upstream side of the flow and giverise to the perturbationswhich have been referred to in the preamble tothe presentdescription.

In the form of embodiment of the invention which is shown in Fig. 4,this drawback is obviated by constructing the part of each of the blades2, which is contiguous with the leading edge of these blades, intheshape of the part 4 which is separated from the blade and is pivotallyfixed thereto at 5, so that it can be directed into the direction of theincident flow. The Mach lines 3 represented in chain-dotted lines, andwhich are produced at the angular transition between each pivoted inletpart 4 and the body 'of the corresponding blade are stopped by theintake part of the next adjacent blade and are thus reflected towardsthe downstream side of the flow, as

ing edges of which are fixed. In an embodiment of this type, the blades4:: maybe shorter than the auxiliary blades formed by the pivoted inletportions 4 of the embodiment shown in Fig. 4.

In the alternative form of embodiment shown in'Fig. 6, the inletportions 4 of the blades 2 are no longer articulated but are flexible,these parts being made of elastic material to that end; In the case ofeach blade, the Mach'line is converted into a network of lines 3b, eachof which has an intensity which is only a fraction of the correspondingvalue in the cases previously discussed.

In Fig. '7, two of the inlet portions or auxiliary blades 4 of Fig. 4have been shown, eachof these'portions'being pivoted with respect to thebody of the corresponding blade 2, To this end, each of these portionsis fixed on a spindle 7 adapted to pivot in the fixed casing 7a of thecompressor (see Fig. 8).

7 One of these auxiliary blades serves as an automatic control for theothers. To this end it is provided with two pressure-tapping points 8,9, located respectively on its intrados and its extrados. These pressuretappings communicate respectively with conduits 12, 13, through thechannels 10,11, formed in the auxiliary blade, and orifices 10a, 11a,drilled in the shaft 7. The conduits 12, 13, start from a fixed box 12awhich surrounds the.

extremity of the shaft 7 on the outside of the fixed casing One of theconduits 12 terminates in the interior of the sealed pressure capsules14. The other conduit, 13 terminates on the exterior of these capsulesin an. air-tight box 15 which encloses them. a

If the pressure at the intrados at point 8 is greater than the extradospressure at the point 9, the pressure capsules expand, whilst theycontract in the contrary case. They take up a mean volume for the casein which'the pressures'at 8 and 9 are equal, that is to say for thecasein which the control auxiliary blade 4 is' directed exactly in thedirection .of the relative flow. 7 In this case, the oil-pressure motor16, the piston 17 of which is coupled .by the circular rod System18which surrounds the casing of the compressor'to levers 19 rigidly fixedto the various auxiliary blades, remains in the position of rest andleaves the auxiliary blades in the correct position which they occupy.In fact,'the distributor piston-valve 20, rigidly coupled to the pressure capsule 14' through the medium of the rod 21, is in the positionshown at which it shuts-.ofi'the 'conduits 22, 23 which communicate withthe respective faces of' the piston 17. An expansion or a contraction ofthe capsules 14, when the mean line of the auxiliary blades 4 does notcoincide with thedirection of the flow, has the elfect -of displacingthe distributor 20, either in one direction :01' the other, thus settingthe piston, 17 into action in the appropriate sense so as to place theauxiliaryblades 4 in the direction of the relative flowQ By way ofalternative, the conduits 10a and 11a,.in-

stead of being drilled side by side in the' shaft 7, could 1 I bedrilled one at each end of this shaft, so that in this case'the conduits12, "13, would be' connected one to, one end of the said shaft, theother to its opposite, end.

It will further be understood that modifications can ing with a sharpsupersonic'leading edge and pivoting about an axis extendingsubstantially at the junction between said portions, meansifor adjustingthe angular position of the pivotal portions relatively to thestationary portions, and means responsive to the differential pressureon both sides of a pivotal portion for controlling the former-mentionedmeans. e

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